The proposed research will examine the contribution of fewer declarative sentences and less frequent conversation to delays in expressive language among children with Down syndrome. Data from more than 10 years of longitudinal observations of communicative development in children with retardation being reared at home will be compare to data from 21/2 years of methodologically-identical observations of typically-developing children learning to talk. Each declarative sentence will be located in each child's data and coded for initiator, turns, shared topic, different and mutual vocabulary, and parent behaviors that may be facilitate learning to converse. The results of the two studies will be the basis for proposing interventions to remediate the deficit in MLU (mean length of utterance) that leads the language skills of children with Down syndrome to lag behind measures of their cognitive functioning.